Method of making friction material



July 1o, 1951 R. W. BROWN METHOD OF MAKIG FRICTION .MATERIAL Original Filed Oct. 14, 1942 2 Sheets-Sheet '2 www Roy 10Q rown Patented July 10, 1951 O F F ICE METHOD F MAKING FRICTION MATERIAL Roy W. Brown, Akron, Ohio, assignor to The Firestone Tire & Rubber Company, Akron, Ohio, a

corporation of Ohio -Original application October 14, 1942, Serial No. 462,060. Divided and this application April 8, l1949, Serial No. 86,376

This invention relates tofriction devices and to friction material and lubricants therefor. The invention also relates to a method of making said friction material, lubricants and friction devices.

'I'his application is a division of my copending application Serial No. 462,060, filed October 14,

cient of friction which is greater than its static coelcient of friction.

Another object is to provide a method of making an improved friction device.

Another object is to provide a friction material having a surface which exhibits a coefficient of kinetic or dynamic friction greater than its coeiiicient of static friction, and to provide a method of making said friction material.

The above and further objects not now specifically enumerated will be manifest in the following description of the invention when considered with the accompanying drawings, in which:

Figure vl is a sectional view of one form of friction device produced by the invention;

Figure 2 is another sectional view, taken on line 2-2 of Figure l; f

Figure 3 is a sectional view taken on line 3 3 of Figure 4, illustrating the mold and vmethod used in making the resilient bushing for the device of Figures l and 2;

Figure 4 is another sectional view illustrating the mold and method used in making the resilient bushing for the device of Figures l and 2;

' Figure 5 is a sectional view ofthe assemblage of parts prior to insertion in the mold of Fig- 'ures 3 and 4;

Figure 6 is a sectional view of a plastic or elastic ring prior to its incorporation in the resilient bushing of the friction device of Figures l and 2;

Figure 7 is a horizontal sectional view of a universal friction device produced by the inven tion, incorporated in the torque tube of an automobile;

Figure 8 is a sectional view of another friction device produced by the invention;

Figure 9 is a sectional view illustrating aimold. and method used in making the resilient bushing of the friction device of Figure 8; and

Figure 10 is a plan view of the fabric lining for the resilient bushing of the friction device of Figure 8 before being inserted intol the mold of Figure 9.

The invention contemplates the production of a friction device having the desirable characteristics set forth in the objects, as well as 4 claims. (ci. 154-130) suitable friction material for such device. The

novel device, which may partake of any conventional external appearance or shape, is distinguished from the prior art by the fact that its` coeiiicient of kinetic o'r dynamic friction is greater than its coefficient of static friction; the term, static friction, is used herein to relate to the friction between two bodies in contact with each other immediately following initiation of motion of one of said bodies relative to said other body, and the term, kinetic or dynamic friction, is used in the usual sense in which it is employed by those skilled inthe art of friction devices. The friction device comprises `a bearing of which the novel friction material provides one bearing surface. The friction material comprises a porous flexible layer, such as a textile fabric, and preferably is backed by an insulating layer of a, resilient, elastic substance, such as rubber, synthetic rubber or other rubber-like substance. The exposed surface of the porous layer, opposite the resilient, elastic backing, provides the bearing surface of the friction material. The porous layer of the friction material is preferably impregnated with and lubricated by a novel lubricating composition, concerning which a detailed disclosure will be presented hereinafter. v

Referring to the drawings, in which similar numerals refer to similar parts throughout the several views, Figures l and 2 lare sectional views of a friction device, inthe form of a pivotal joint I I. This type of joint is particularly adapted for use in the steering linkages of vehicle wheels, although it may advantageously replacel other mechanical linkages. The pivotal joint II comprises an inner bearingr member I2, illustrated as a hollow ball, an outer housing I3, and an intermediate bushing I 4. The ball member I2 may take various forms so long as it has a substantially spherical bearing surface, and may be solid rather than hollow. The outer casing may also take various forms, being an integral part of the steering cross link I5, as shown, or an independent structure. The bearing member I2 has an integral stud I6 which may be attached to one of the pivoted parts. The bushing I4 comprises a resilient outer layer of rubber I'I, or material having -substantially similar properties, and an inner lining I8.

The lining I8 is preferably made of a porous, flexible material impregnated with a lubricant suliicient in amount and having such characteristics that the joint will be properly lubricated for the full useful life of the joint. The flexibility of the lining I8 and the resiliency of the rubber layer Il impart to the joint noise and vibration insulating properties and allow slight irregularities on the inner bearing member I2, thus eliminating the necessity of machining said member.

''he member I2 may therefore be made of an unmachined, stamped or forged metal part. The rubber layer I1 oi the bushing I4 has an integral extension or skirt I9 extending beyond the housing I3 and surrounding the shank of the stud I6 of the inner bearing member I2. The skirt I9 terminates in a ilange 2I carrying a lubricated disk 22 of lining material, which is a composition similar to the lining I8 of the ball joint. The skirt and ilange lining material are resiliently urged against the under surface of an eye 23 on the end of a steering link or other member (not shown), which is connected to the link I by means of the joint Il', in order to provide a suitable dirt seal to exclude foreign matter from the ball joint.

As will be pointed out in further detail hereinafter, thebushing I4 is molded and vulcanized to a predetermined form, size and shape substantially complemental to the inner contour of the housing I3. Then the ball joint and molded bushing are inserted through the aperture in the lower side of the housing. A plate-like disk 24 is placed beneath the joint and bushing, and a ange 25 is peened over to retain the disk 24 in fixed position and seal the lower portion of the joint. If desired, the hollow space formed by the hollow ball I2 and the disk 24 may be filled with a reserve supply of lubricant during the assembly of Kthe Joint.

The lining I8 is preferably fabric which has been impregnated with the novel lubricant of the invention, and the backing layer I1 is preferably vulcanized rubber or synthetic rubber, whereby there is produced in the joint, when the lining is in frictonal contact with the metal ball I2, a

dynamic coefficient of friction that is greater than the static coefficient of friction of the joint. 'I'his novel friction characteristic of the joint is very important and desirable in steering linkages, since it greatly aids the driver of the vehicle in maintaining a. desired course at high speeds de spite intermittent external side forces due to wind and shifting of the vehicle on account of uneven road conditions. With steering linkages having this peculiar friction characteristic there is substantially no extra "breakaway effort required to initiate steering controlthere is less eiort required to initiate steering movement than is necessary to maintain steering movement. Accordingly, the driver needs only to apply a steady, smooth force while changing the steering angle of the dirigible wheels of the vehicle, whereby he is able to maintain a predetermined course at high speed without fatigue.

For the purpose of providing a stable and rattle-free joint, means may be provided to urge the shank of the stud I6 to a central position relative to the outer housing I3. To this end, the outer housing may be provided with recesses I3a at opposite sides thereof and adapted to receive lugs 26 which are integral with the skirt I9 of the bushing. The engagement of the lugs with the recesses prevents relative rotational movement between the outer housing and the bushing, and therefore prevents Charing of the rubber layer thereof.

The lower end of rubber layer I1 is provided with an annular ring portion 21 of rubber stock softer, when vulcanized, than the layer I1 itself. The line of demarkation between these two stocks is indicated by the cross-hatching. During the manufacture of the rubber part the thickness and resiliency of this ring may be altered, so that when disk 24 is fixed in predetermined assembled relation the bushing I4 will be placed under a predetermined amount of compression, tor the purpose of providing a snug t between the lining Il and the ball I2. It is to be understood in this connection, however, that the rubber part I1 is molded to a shape substantially complemental to the inside contour of the housing before assembling, and that the amount of compression of the assembled joint is only suil'icient to maintain a stable joint. The relative position of the ball 'with respect to the casing is determined by the shaping of the molded rubber part and not primarily by the amount of compression to which the lining is subjected.

As shown, the pivotal connection II is capable of moving farther in the plane illustrated in Figure 1 than in the plane at right angles thereto, illustrated in Figure 2. 'I'he necessity'for this movement in one plane and the limitation in the other plane will be understood when it is remembered that greater angular movement is necessary in some planes than in other planes in order to accommodate all of the steering movements for the various possible positions of the wheels relative to the body of the vehicle.

Figures 3, 4, 5 and 6 illustrate the method of making the pivotal joint shown in Figures 1 and 2. Although bushing I4 appears to be round in Figures l and 2,1t is to be understood that where the pivotal connection is to be installed in a steering linkage where the pivotal movement in one plane isto be greater than in another plane at right angles thereto, the skirt or extension portion I9 of the bushing is made out-of-round or substantially elliptical.

In Figure 3, where the method of molding the bushing is shown, this modified out-of-round extension or skirt is shown. It will be understood that the methods of making a round skirt or an out-of-round skirt are exactly the same except for the shape of the mold cavity. It-is possible, of course, to permit greater movement in one plane than another by using an annular top on the outer housing of the joint and an annular bushing to ilt, but it would be' necessary to have the diameter suillcient to accommodate the maximum angular movement. In some instances this arrangement might cause a sacrifice in stability of the joint. Hence, the preferred, elliptical modified form of bushing is shown in Figure 3, the skirt part I9 being vulcanized in the out-of-round shape while the lower part of the bushing is vulcanized in the round shape and size it will have in the assembly., The purpose of this arrangement is to permit more movement in the plane shown in Figure l than the permissible movement in the plane shown in Figure 2, the latter plane being that of the lugs 26.

Referring to Figure 5, a rubber ring A may be made by suitable known methods, such as by forming a tube and'then cutting it into narrow rings, or by sheeting and dieing rings of the desired thickness and resiliency. The thickness and resiliency of the ring A, which corresponds to the annular ring 21 of Figures 1 and 2, and becomes an integral part of the bushing of the joint after vulcanization, will determine the precompression of the bushing when assembled in a joint.

Next, a suitable bearing fabric I8 is prepared by coating one side thereof by dipping in, or otherwise impregnating with, an adhesive composition which increases the adherence of the fabric to rubber. This fabric strip is cut into the proper length and width and wrapped around the-enlarged spherical portion of a mandrel 28,

Athe length of the fabric strip being such that the ends overlap by an amount between one-eighth and one-fourth of an inch. The overlapping portions of the fabric are suitably cemented together to hold them in position. Thereafter, the rubber cylindrical member B is placed around the fabric. This may be done by wrapping asection of gum strip over the fabric or alternatively, if desired, preparing a tube of rubber stock and slipping the same over the fabric I8. The mold l insert 29 is then assembled on the extension of the mandrel 28. The rubber part C, shown in unstressed condition in Figure 6, is prepared by tubing and cutting, or by sheeting and dieing a rubber stock to produce a ring similar in shape to part A, except that part C is somewhat greater in thickness. Thereafter, a fabric disk D, which has been prepared by dipping one side thereof in, or otherwise impregnating a suitable material to cause it to adhere to rubber, and the other side of which has been impregnated with a suitable lubricant is placed `against the rubber ring C with the adhesive impregnated side against the ring C. The collar 3| isthen placed on the extension of the mandrel 28, and a nut 32 is tightened up in any suitable manner to compress the part C into the shape shown in Figure 5. In assembling the parts C and D it is important that they be arranged in concentric relation. To hold the mold insert 29 rigidly in position on the mandrel 26 a key 33 is placed in a slot 34 of the insert and pushed into a slot 35 on the shank of the mandrel 28.

The mandrel 28, with the component parts of the bushing assembled thereon, is then placed in the mold, as shown in Figures 3 and 4, and vulcanized. During the vulcanization process the parts A, B, and C are vulcanized into an integral unit, the space between the parts B and C b ecoming bridged by the ow of rubber in the cavity of the mold to form the extension or skirt i9 and the lugs 26 of the bushing I4. The vulcanized bushing is thereafter removed from the mold, and the mandrel 28 and other mold insert parts are removed therefrom. Before the temperature of the bushing has dropped below approximately 140 F. the exposed fabric surfaces of the lining I8 and disk 22 are lubricated with a suitable lubricant, such as the novel lubricant comprising graphite and castoroil, hereinafter described. Alternatively, the bushing may be allowed to cool, if desired,l and treated with melted solid lubricant to impregnate the exposed fabric surfaces, by the preferred lubricant impregnating technique described in detail hereinafter.

Another embodiment of the friction device of the invention is a universal friction device 36 shown in Figure 7 as incorporated in the torque tube of an automobile. Within the torque tube 31 is a shaft 38 that extends to the differential mechanism in the axle housing (not shown), said shaft 38 being connected to a shaft 39 from the automobile engine (not shown) through the `agency of a universal joint 4I of the usual Wellknown construction, said universal joint being positioned adjacent to the intersection of the automobile frame cross braces 42, 42. There is a ball bearing43 positioned between the torque tube 31 and the shaft 38 adjacent to universal joint 4I. Threaded into the forward end of the torque tube 31 and abutting the outer race of bearing 43 is the tubular, rear portion 44 of a movable element of the friction device 36, the forward end portion of said element being of concave-convex shape, as shown at 45, and positioned concentrically with relation to the center of the universal'joint 4I Vulcanized to the concave and to 'the convex surfaces of portion 45 are respective layers of resilient rubber composition 46, 46 and bonded to the latter are facings 41, 41 of a porous material, preferably textile fabric impregnated with the novel lubricant described in detail hereinafter. The` arrangement is such that the rubber layers 46 constitute a resilient backing between the friction facings 41 and the surfaces of the concave-convex structure 45. There is an annular sealing gasket 48 interposed between portion 44 of the movable element and the enclosed hub portion of the universal joint 4I. Preferably, the tubular portion 1 44 is permanently secured to the torque tube 31,

as by the welding indicated at 49.

Secured to the cross braces 42 of the frame, as by means of bolts 5I, is an annular plate 52 that is positioned substantially in the medial plane of rotation of the universal joint, and formed about the axial aperture of said plate is a concave-convex formation 53 that is disposed exteriorly of the similar shaped structure 45 and is concentric with the center of the universal joint. Normally the friction facing 41 on the convex side of portion 45 is in abutting relation to the concave face of formation 53, the latter constituting a socket for the portion 45. Positioned concentrically within the latter is an annular, concave-convex shell 54 that encircles the universal joint and has its convex face in abutting relation to the friction facing 41 on the concave face of portion 45. Shell 54 is formed with a radially outwardly extending marginal flange 55 that is disposed parallel to plate 52' and in spaced relation thereto, said flange being secured to said plate by a plurality of bolts 56, 56. There is a coiled compression spring 51 between the head of each bolt 56 and the adjacent face of flange 55, the arrangement being,r such as to urge the shell 54 axially toward the portion 45, with the result that there is at all times good frictional contact between the friction facings 41 on both sides of portion 45, and the concave-convex structures 53 and 54 that engage said facings.

A flexible annular sealing ring=58 of rubber or similar material embraces the tubular structure 44 of the movable member of the device and the adjacent margin at the inner circumference of the structure 53 to seal the device from dirt and other foreign materials and to prevent the possible escape of lubricant between the said members.` At the opposite side of the device is a closure consisting of an annular dished plate 59 that is secured, at its outer circumference, to the plate 52, and at its inner circumference carries an annular sealing gasket 6I that embraces the drive shaft 39. When the closure plate 59 is removed, the heads of bolts 56 are exposed so that by the adjusting of said bolts the force of springs 51 may be varied to alter the friction between the friction facings 41 and the structures that engage them. The arrangement is such that any relative movement between the running gear of the automobile and the frame thereof, such as torque and thrust reactions, are translated through the torque tube-to the friction device at the universal joint, which device is universalin its ability to offer determinate and resilient frictional resistance to said relative movements. Because of the utilization of the novel friction material 46-41 in this friction device, there is no tendency for the latter to bind, and it efficiently dampens the said relative movements, whereby the. automobile proceeds over a rough road more smoothly.

The friction material for the friction device 3i is made by adhering one face of the porous facing material 41 to the resilient backing material 4B, bonding the surface of the backing material opposite the facing material to the concave and convex surfaces of the portion 45, as shown, and then imprcgnating the `exposed surfaces of the facing material 41 with the novel lubricant. In a preferred method of making the preferred construction of device 36, a textile fabric is utilized for facing material 41, and this fabric is adhered to a suitable rubber composition by calendering. The friction material 46- 41, so prepared, is than positioned upon the opposite surfaces of portion 45, as indicated in Figure 7, and bonded thereto, preferably by vulcanization; the surfaces of the metal portion 45 are preferably treated to improve the adhcsion of the rubber layers 46 thereto, as by brass plating and/or coating with an adhesive cement. After vulcanization of the rubber layers 46, the exposed surfaces 41 are impregnated with the novel lubricant. as in the preferred manner hereinafter described.

A further modification of the friction device is shown in'Figure 8, in which a pivotal joint G2 comprises a ball-shaped inner bearing member B3 and an outer casing G4, the latter being simply and cheaply made of stamped sheet metal. Between the bearing member and the casing is a bushing 65 of the novel friction material,said bushing comprising, a resilient outer layer of rubber 66, or material having substantially similar properties, and an inner lining 61, preferably of textile fabric. The bushing 65 is similar in function and operation to the 4bushing I4 of the.

joint Il of Figures 1 and 2. The joint 62 is simpler than the joint Il in comprising a cheap, independent casing 84, which may be pressed around the assembled bushing and bearing member. The ball joint 62 may pivot throughout a wide range.

'I'he bushing 65 is molded in a suitable mold il, shown in Figure 9. after the fabric 69, of the friction material, and a suitably shaped rubber stock, for forming layer 66, have been assembled on asuitable mandrel 1I. Figure l0 shows the orange peel shape in which the fabric is preferably cut before it is assembled in the mold. During the early stages of vulcanizing the bushing the rubber stock flows to illl out the mold cavity and assumes the shape shown in Figure 9. The vvulcanized bushing is then preferably treated in a suitable manner to impregnate the exposed surface of the fabric 69 with the novel lubricant. before the bushing, bearing. member and casing are assembled.

LUBRICANT lubricant comprises a basic ingredient which is an emcient lubricant, which does not swell or otherwise deleteriously affect vulcanized rubber or synthetic rubber, and which contains no appreciablequantity of a substance that may promote the corrosion of metal used in bearing or housing parts of a friction device.

A raw castor oil selected to contain a low fat acid content has been found to possess the qualities desired for the basic ingredient of the lubricant. This preferred castor oil is of a quality equal to a castor oil suitable for medicinal uses. A part or all of the castor oil of the lubricant may be replaced by derivatives of castor oil. For example, the viscosity and pour point of the lubricant may be lowered by utilizing acetylated castor oil. Also, the viscosity of the lubricant may be increased by employing hydrogenated castor oil Vin the lubricant. Other lubricating substances, besides castor oil derivatives. may be added to the lubricant, such as flake or colloidal graphite, various waxes, and modifiers and other special materials which specifically improve the properties of the lubricant.

Example 1 parts of a commercial preparation of colloidal graphite in castor oil. Such preparation suitably contains 10 per cent of colloidal graphite and 90 per cent of raw castor oil. of the quality indicated above. The colloidal graphite functions in a friction device to penetrate to all p0rtions of the device accessible to the lubricant and to aid the castor oil in efficiently lubricating allmoving surfaces contacting the bearing surface of the friction material impregnated with the lubricant. The flake graphite fills the pores in the-bearing surface of the friction material to provide a more uniform bearing surface "the part hasdropped below 140 F.

.Example 2 An exampley of asolid or substantially solid lubricant, which is better suited to many friction devices than a liquid lubricant, may be prepared by adding certain solid or semi-solid materials, preferably of a waxy nature, to a castor oil-graphite composition similar to the preceding liquid lubricant. A suitable solid lubricant may contain the following ingredients:

Per cent by weight Beeswax 24 Lanolin 24.5 Castor oil v 20 Flake graphite 0.5 10% colloidal graphite-90% castor oil 25 The novel lubricant possesses thixotropic properties, whereby itacts as a solid at ordinary atmospheric temperatures and under low stress Metallic soaps mixture conditions but acts as a liquid at localized regions in a bearing when relatively high stresses are brought to bear upon it. Thus, the lubricant does not liquify to the point of flowing out of the joint or friction material but only to the extent of providing good lubrication to the bearing. The lubricant possesses this desirable lubricating characteristic even at very low temperatures. The waxy ingredients, beeswax and lanolin, ofthe lubricant are compatible with the other ingredients thereof and are water insoluble.

The metallic soaps mixture is essentially composed of aluminum soaps, the term soaps being used broadly, said soap being dispersible in castor Y oil or a castor oil derivative. A preferred composition is a special aluminum soap composition dispersible in castor oil. An example of such composition is a dispersion of approximately 50 per cent of the aluminum-containing reaction product of a mixture of an aluminum compound, sulfuric acid and the fats normally present in raw castor oil, and approximately 50 per cent of castor oil. The metallic soaps mixture is compa tible with the other ingredients of the lubricant and is insoluble in water. The mixture improves the lubricating lm strength of the lubricant and presents it from losing its high lubricating eiliciency at very low temperatures, by tending to inhibit the hysteresis of viscosity of `the castor oil or castor oil derivative present inthe lubricant.

The mixture also increases the viscosity of waxes, such as beeswax and lanolin, at temperatures above their melting points, whereby the lubricant does not tend to oW from a bearing utilizing the same when the bearing temperatures are high.

The above solid lubricant may suitably be liquied by heating to 20G-225 F. for impregnating friction material.

A further example of a solid lubricant, and one lthat is preferred for general usage in the friction material and devices produced by the invention, possesses approximately the following composition:

Per cent by weight The iiake graphite, colloidal graphite-castor oil and metallic soaps mixture have already been described in connection with earlier examples of the lubricant. The hydrogenated castor oil is a hard, waxy material, compatible with the other ingredients of the lubricant and unaffected by water or petroleum products. This waxy substance makes the lubricant substantially solidat ordinary atmospheric temperatures and is an effective lubricant.

The calcium dichlorostearate is a special additive or modifier functioning to improve the lubrieating film strength of the lubrican, to increase the viscosity of the same at high temperatures and substantially to inhibit the hysteresis of viscosity of the lubricant at low temperatures. This calcium compound cooperates with the special additive effect when combined in the lubricant. The oxidized and polymerized castor oil is a viscous material, which may be sticky and have a spongy structure. It may be prepared by heating and blowing castor oil. This modified castor oil is very effective in controlling the friction characteristics of the lubricant, since a very small proportion of it in the lubricant imparts increased friction properties thereto. This lubricant additive also tends to increase the ratio of the static friction/dynamic friction of the lubricant, whereby it is possible to prepare a lubricant having better balanced frictional properties throughout a wide temperature range. Thus, for instance, the lubricant in this example, by reason of the presence of the modified castor oil therein, possesses substantially the same desirable frictional characteristics at temperatures below 0 F. as it possesses at higher and more normal atmospheric temperatures.

The lubricant of this example is insoluble in water, petroleum products and vulcanized rubber. It is a hard wax at room temperatures,

softens appreciably around 140 F. and is thixotropic, Beyond its melting point of approximately 186 F. it is liquid, having excellent lm strength and wetting properties. This combination of properties prevents wastage of lubricant by i'low from the bearings or from mechanical abrasion incidental to immersion in water and dirt, and when loaded dynamically it provides adequate lubrication. Actual tests have indicated that the coefficient of friction of a friction device lubricated with this lubricant decreases at temperatures below 32 F. Thus, for example, a vehicle employing the preferred type of lubricant in steering link joints is more easily steered in cold weather than in temperate Weather. 'Ihe aluminum soap composition of the metallic soaps mixture to impart modied properties to the lubricant in addition to theproperties expected by the addition of eaci modifier singly. In other Words,k these two modifiers produce more than an lubricant, by reason of its physical properties enumerated above, Iwill normally remain in friction material impregnated therewith for the useful life of the friction device embodying the friction material.

Example 4 Another example of a preferred solid lubricant, which is similar to the lubricant of Example 3 except that it contains no graphite, is a composition having the following formula:

Per cent by weight Calcium dichlorostearate 1.0 Castor oil 31.0 Metallic soaps mixture l4.0 Hydrogenated castor oil 63.5 Oxidized and polymerized castor oil 0.5

The preferred lubricant of Examples 2, 3 and 4 maybe generically expressed in the following formula, in parts by weight, wherein fractional parts are disregarded in the case of the major ingredients:

Castor oil 29 to 46 A waxy lubricant of the group consisting of hydrogenated castor oil, beeswax and lanolin 48 to 64 An aluminum soap 2 to -3 IMPREGNATING FRICTION MATERIAL A preferred method of impregnating the friction material with the lubricant will now be briefly described. This method gives uniformly satisfactory impregnation with any of the specific types of lubricants disclosed above, and is especially effective with the solid lubricants of Examples 2, 3 and 4.

The molded friction material, in which the rubber or rubber-like layer is vulcanized or cured, is carefully protected from coming into contact with water, steam or petroleum products, especially oils and greases. The material is actually impregnated in the liquefied lubricant contained in a steam heated kettle designed to maintain the temperature within a denite range to insure uniform impregnations; a temperature of 200- 220 F. has been found satisfactory for lubricants similar to those disclosed in Examples 2, 3 and 4. The kettle is preferably provided with means to maintain a constant liquid level above the parts being impregnated and means for circulating the liquefied lubricant over around the said parts. The parts are preferably suspended in the lubricant in the kettle by means of a centrifuge basket, Within which the parts are positioned. An impregnation time of approximately minutes has been found to be satisfactory for a variety of differently constructed parts, but a variation in this gure may be desirable for specific lubricants or friction materials.

The completely impregnated parts are then cleared of excess lubricant by removing the basket containing the parts from the kettle and immediately centrifuging them for a short period of time, suitably a minute or two. The impregnated friction material parts are then ready for assembling in the friction devices for which they have been designed. y

From the foregoing discussion it is seen that the invention relates to the production of any friction device or friction material possessing a coefficient of kinetic or dynamic friction which is gretaer than its coefficient of static friction. The friction material possesses this friction characteristic, even Without the aid of the novel lubricant, when it comprises a layer of a porous bearing material backed by an insulating layer of a resilient, elastic material. Examples of this type of friction material includes a structure comprising a layer of textile fabric adhered to a backing layer of vulcanized or cured rubber or synthetic rubber. The preferred novel lubricant possesses such friction characteristics that it may impart to a friction material a coefficient of kinetic friction greater than its coefficient of static friction, even though the friction material does not comprise a resilient, elastic backing layer. For example, friction material consisting of a layer of textile fabric directly backed by a rigid casing or housing of a friction device shows, when impregnated with a preferred lubricant, e. g. the lubricant of Example 3, a coefficient of kinetic friction which is greater than its coefficient of static friction.

As an indication of the specific friction characteristics of a preferred friction material, one

example is hereby given. A friction material comprising a layer of woven cotton fabric adhered toa backing layer of vulcanized rubber was impregnated with a lubricant similar to the lubricant of Example 2. The impregnated material was found to possess a ratio of kinetic/static friction of approximately 3/ 1.

Wide variations in the design of the friction device and in the specific nature and proportions of the ingredients of the lubricant are included within the scope of the invention, as will be apparent to those skilled in the art, who may make such variations in order to attain desired specific results.

What is claimed is:

1. The method of making friction material comprising calendering a vulcanizable elastic composition into one side of a flexible friction material, vulcanizing said vulcanizable composition to a metal backing member, and impregnating the exposed uncalendered side of said friction material with a liquefied lubricant.

2. 'Ihe method of making a friction device comprising calendering a vulcanizable elastic composition into a fabric material, vulcanizing said composition to a metal backing member, and impregnating the uncalendered side of said fabric with a liquefied composition of graphite and castor oil.

3. The method of making friction material comprising adhering one face of layer of a flexible, porous bearing material to an insulating layer of4 a vulcanizable resilient, elastic substance, vulcanizing the insulating layer to a.' metal backing member, and impregnating the exposed face of the bearing material with a liquefied lubricant.

4. The method of making friction material comprising adhering one face of a layer of' a flexible, porous bearing material to an insulating layer of a vulcanizable resilient, elastic substance, vulcanizing the insulating layer to a metal backing member, and impregnating the exposed face of the bearing material with a liqueed thixotropic lubricant having substantially the following composition in parts by weight:

Castor oil 29 to 46 A waxy lubricant of the group consisting of hydrogenated castor oil, Beeswax and lanolin 48 to 64 An aluminum soap 2to 3 ROY W. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,430,143 Barefoot Sept. 26, 1922 1,801,666 Geer Apr. 21, 1931 2,026,272 Danser Dec. 31. 1935 2,246,101 McEnany June 17, 1941 FOREIGN PATENTS Number Country Date 348,600 Great Britain May 6, 1931 

3. THE METHOD OF MAKING FRIOTION MATERIAL COMPRISING ADHERING ONE FACE OF LAYER OF A FLEXIBLE, POROUS BEARING MATERIAL TO AN INSULATING LAYER OF A VULCANIZABLE RESILIENT, ELASTIC SUBSTANCE, VULCANIZING THE INSULATING LAYER TO A METAL BACKING MEMBER, AND IMPREGNATING THE EXPOSED FACE OF THE BEARING MATERIAL WITH A LIQUEFIED LUBRICANT. 